Aneurysmal subarachnoid hemorrhage (SAH) is a highly morbid condition - much of which is due to delayed cerebral ischemia (DCI), which is caused by a combination of large-artery vasospasm and microcirculatory deficits including autoregulatory dysfunction, microvascular thrombosis, and blood-brain- barrier (BBB) breakdown. Conditioning refers to the phenomenon whereby exposure of the brain to a sub- lethal stimulus renders it more resistant to a subsequent lethal stimulus. Most have examined the protective effects of conditioning on neurons, but we and others have established that the cerebral vessels are also a target. Given that DCI is caused by wide-ranging vascular deficits (from large arteries to the microcirculation) and that conditioning appears capable of preventing these deficits, a conditioning- based therapeutic strategy applied to SAH holds great promise. In our past study, we showed that powerful endogenous protective mechanisms against DCI exist, can be induced by a conditioning stimulus (brief hypoxia prior to SAH; termed hypoxic preconditioning or HPreC), and are dependent on endothelial nitric oxide synthase (eNOS). In a pilot study, we show that the same stimulus (hypoxia) when initiated at a clinically relevant time point (3h after SAH; termed hypoxic postconditioning or HPostC) provides similarly strong DCI protection. The molecular inducer(s) of this protection, however, are unknown. We believe sirtuin1 (SIRT1) is a key inducer, as hypoxia augments SIRT1 expression, HPreC-induced DCI protection is lost with the SIRT1 inhibitor EX527, and the SIRT1 activator resveratrol mimics the DCI protection afforded by HPreC and HPostC. The long-term goal of our project is to test the hypotheses that HPostC induces robust and multifaceted DCI protection, SIRT1 is a key inducer of this protection, and SIRT1 activation is a novel strategy for SAH that has exceptional translational potential. The Specific Aims are 1) Determine the breadth and sustainability of HPostC-induced DCI protection; 2) Test whether SIRT1 is a key inducer of HPostC-induced DCI protection; and 3) Determine the translational potential of SIRT1 activation in SAH. Methods used include: a) assessment of SIRT1, eNOS, MMP-9, TIMP-1, and TF expression and activity; b) assessment of SAH-induced vasospasm, microcirculatory deficits (autoregulatory impairment, microvessel thrombosis, and BBB breakdown), and neurological deficits in mice; c) assessment of SAH-induced vasospasm, microcirculatory deficits, neurological deficits, neuronal cell death, and long-term neurobehavioral deficits in rats; d) pharmacologic and genetic inhibition of SIRT1; and g) pharmacologic and genetic augmentation of SIRT1. If successful, these studies will result in an improved understanding of the breadth, mechanism, and sustainability of HPostC-induced neurovascular protection in SAH, will identify SIRT1 as a novel and druggable therapeutic target for DCI, will determine the translatability of SIRT1-directed therapeutics for DCI, and will identify CSF and serum biomarkers that can be used to directly test for pharmacodynamic efficacy in future human studies.